Generally, an excavator is equipped with a front work device such as a boom, an arm, a bucket etc. at an upper turning body, and individually or simultaneously operates one or more of corresponding work devices with a pressurized fluid discharged in one or more hydraulic pump to perform various multiple works such as an excavation work, ground leveling, material collecting work, load work etc. Here, a multiple work means a work that is performed through simultaneously operating more than two hydraulic devices among a boom, an arm, a turning motor.
Meanwhile, Korean Patent Publication NO. 10-2006-0068668 is related to a hydraulic control device controlling a multiple movement simultaneously operating a boom and arm of excavator, as a boom valve automatically increases or decreases a boom speed according to an operation level of valve, preferentially provides a lot of pump flux to a boom in case of multiple work such as a load work or evenness work in which a change of boom operation load is bigger than a change of arm operation load.
Such exiting art necessarily needs a skilled operation of worker because a boom and arm needs to be accurately moved along a ground when ground leveling or material collecting work which is one of main works of construction equipment like excavator, and has drawback that is increase of worker's tiredness when such operation is repeated.
Therefore, an equipment that is equipped with a float circuit that connects a boom cylinder rod or head hydraulic circuit with hydraulic thank to descend a boom by self-weight of work device instead of pump pressure or ascend a boom by ground reaction force when worker intends to facilitate work is being developed.
However, because a return operation in which a boom is lifted for a bucket to be moved after an operation in which bucket moves along a ground is needed even in such case, a drawback still exists, in that work is performed by an operation of a boom and arm.